In recent years, precious metal thin films of ruthenium, platinum, iridium, etc. or oxide films of these precious metals have been used as electrode materials of electrical and electronic parts, such as capacitors of ICs and LSIs. This is because they have especially excellent electrode characteristics when these precious metals are formed as thin film electrodes, and in particular, ruthenium and ruthenium oxides are receiving attention because they are considered to become main materials for thin film electrodes in the future.
In addition to sputtering, the chemical vapor deposition method (hereinafter referred to as the CVD method) is used as methods of manufacturing ruthenium and ruthenium oxide thin films. This is because the CVD method makes it easy to manufacture uniform films and besides the CVD method is excellent in step coverage.
Among other metal compounds, organic metal compounds which have low melting points and are easy to handle are often used as raw materials used in the CVD method. A bis(cyclopentadienyl)ruthenium derivative is known as a CVD material for manufacturing ruthenium thin films.
The bis(cyclopentadienyl)ruthenium derivative is obtained by introducing a substituent, such as an alkyl group, an acetyl group and a carbonyl group, in either or both of the cyclopentadienyl groups of bis(cyclopentadienyl)ruthenium. The reason why this bis(cyclopentadienyl)ruthenium derivative is useful as a CVD material is that, in addition to a high vapor pressure, this derivative has a low melting point and is in a liquid state at room temperature, with the result that this derivative is excellent in convenience in handling in the thin film manufacturing process. The reason why the bis(cyclopentadienyl)ruthenium derivative has such characteristics is that bis(cyclopentadienyl)ruthenium, which is the basic substance of this derivative, basically has properties which are desirable as a CVD raw material and because it is possible further lower the melting point and the steam pressure by introducing a prescribed substituent.
Although as described above, bis(cyclopentadienyl)ruthenium itself is useful as a CVD material, it can be thought that in the future bis(cyclopentadienyl)ruthenium will be more valuable as a material for manufacturing bis(cyclopentadienyl)ruthenium derivatives.
There is known a method of manufacturing a bis(cyclopentadienyl)ruthenium which involves synthesizing a bis(cyclopentadienyl)ruthenium by causing ruthenium chloride, cyclopentadiene and zinc powder to react in an alcohol solvent, removing trace amounts of impurities by use of column chromatography etc. and thereafter purifying the bis(cyclopentadienyl)ruthenium through recrystallization in an organic solvent (for the details of the above manufacturing method, refer to Journal Chemical Society. Dalton, (1980), 1961-1964 and Journal of Organometallic Chemistry, 288 (1985), 341-348). The reason why in this synthesis method, zinc is caused to be present in a reaction system is that zinc has a catalytic action to the synthetic reaction of bis(cyclopentadienyl)ruthenium.
However, this publicly known conventional method had the problem that the yield (percentage to the ruthenium chloride as a raw material, in terms of molar ratio) of manufactured bis(cyclopentadienyl)ruthenium is about 75%, a relatively low value. Furthermore, the above-described purification by recrystallization not only requires a large amount of solvent, raising the cost of manufacturing, but also makes it difficult to recover ruthenium which is lost in the solvent during the purification step. In addition, in the conventional method nonvolatile impurities sometimes got mixed in refined ruthenium, though in trace amounts.
The present invention was made against the above-described background and has as its object the provision of a manufacturing method by which a high-purity bis(cyclopentadienyl)ruthenium can be manufactured at a high yield.